Extension cords are widely employed to provide power to tools and equipment which are remote from electrical outlets and power sources. The extension cords are routinely placed under significant stress, and therefor the connector and plug housings have been improved over the years to include means to securely clamp the cord while minimizing the strain on the terminals. NEMA connectors and plugs generally include an internal mechanical clamp terminal that cooperates with the housing or body to hold a conductor in place. Contact pressure for the clamp terminal is generally provided by a screw threaded through a contact lug which urges the conductor against a current bar, contact tang, or other current carrying element. Examples of such devices include both the 20 and 30 amp locking plugs and connector bodies manufactured either by Marinco Industrial Group of Napa, Calif., or Hubbell Incorporated of Milford, Conn.
Improvements in electrical terminals have been made for use in high density terminal busses. Several United States patents teach the use of electrical connectors of a type that includes a bus bar with a loop-shaped clamping spring fabricated from flat spring material. The connectors typically include a contact portion in electrical contract with the bus bar and a clamping portion extending to the bus bar and curving away from the back of the clamping spring. The clamping spring further includes a curved backward spring segment contiguous with the back of the spring and with the contact portion. The clamping portion has a recess, from which the head of the bus bar extends, such that an edge of the clamping recess clamps an electrical conductor against the underside of the bus bar when the conductor is inserted between the bus bar and the edge of the clamping recess.
The springs have themselves become the focus of rapid development. For instance, U.S. Pat. No. 5,816,867 to Davidsz et al., shows a curved wire spring clamp for use in an electrical terminal. Apertures in the clamp approximate a triangular cantilever and are centrally placed along each leg portion near a constrained curved portion of the spring to change the spring's bending characteristics and distribute the bending stress more evenly throughout the length of the spring, thus reducing the peak bending stress level as compared with an equivalent spring design without apertures.
U.S. Pat. No. 6,010,376 to Kollmann, teaches a low profile connector having a clamping spring with a low structural height. Actuation of the clamping spring for inserting the end of a conductor requires insertion of a tool (generally a screwdriver).
U.S. Pat. No. 6,283,801 to Guinda et al., shows a spring connection terminal for an electrical device which includes a conducting support part fixed to a main conducting part, and at least one clamping spring folded into the form of a loop and provided with a clamping window inside which a flange of the support part passes. It further includes a spring stop folded so as to be housed inside the spring loop and which forms a guide for guiding the wire adjacent to the flange. The device requires insertion of a screwdriver head to insert a conductor.
U.S. Pat. No. 6,595,809 to Matsumoto et al., discloses a high density electrical bus employing a connector having toggle switches that engage clamping springs. When the toggle arm is pushed inwardly, the spring clamp opens to accommodate a wire conductor; and when released, the conductor is captured. The assembly is suited for use in a linear array of terminals but not for a NEMA connector or plug.
U.S. Pat. No. 6,428,339 to Davidson et al., teaches a lockable electrical cord connector unit having a cylindrical connector housing made of electrically non-conductive material. A locking control ring telescopes over the connector housing and is mechanically connected to a structure within the connector housing that allows male electrical connector members extending from the housing to be locked into a female electrical socket. In an alternative embodiment the connector housing may have female sockets that can lock onto a male electrical terminal by using the same locking control ring structure. A second alternative embodiment provides for the connector housing to be an adaptor having male electrical terminal prongs extending from one end and having a female electrical socket formed in its other end. The locking ring allows both ends to be locked to mating electrical terminals.
The foregoing patents reflect the current state of the art of which the present inventor is aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicant's acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.
In fact, despite the advances in spring clamps for high density terminal busses, there remains a need to provide a locking plug and/or connector body having means for efficient (e.g., straight-in) insertion of a conductor for termination in the connector/plug body, wherein no tool is required to bias a clamping spring nor any screw engaged to provide clamping pressure on the conductor.